strategies based on threats
DESCRIPTION
Strategies Based On Threats. Ling Zhao University of Alberta March 10, 2003. Comparative evaluation of strategies based on the values of direct threats by Tristan Cazenave in Board Games in Academia V, Barcelona, 2002. Outline. Motivations Direct threats Thermograph Threat strategies - PowerPoint PPT PresentationTRANSCRIPT
Strategies Based On Threats
Ling Zhao
University of Alberta
March 10, 2003
Comparative evaluation of strategies based on the values of direct threats by Tristan Cazenave in Board Games in Academia V, Barcelona, 2002.
Outline
Motivations Direct threats Thermograph Threat strategies Experimental results
Motivations
Apply combinatorial game theory to Go
- independent subgames
- approach the best stategy
Direct threats
Each subgame has at most two moves
Root of the tree
Black: 22 points
White: 15 points
Value: 7 points for black
Sequence after two black moves
Black: 25 points
White: 14 points
Value: 11 points for black
Direct threat: 4 values
A, B, C, D with A >= B >= C >= D
Denoted as (A, B, C, D)
After one black move
=> (A,B)
After one white move
=> (C,D)
Problem model
Given a set of independent subgames with direct threats, how to compute good moves fast and accurately.
(A1,B1,C1,D1)
(A2,B2,C2,D2)
. . .
(An, Bn, Cn, Dn)
Choose which subgame to play a move?
Thermograph
Temperature: 6.5 Mean value: -4.5
Thermograph for direct threat (4,0,-6,-16)
Strategies
Optimal stategy: brute force (NP-hard?) BMove: compare the best Left move
(A,B,C,D) => value B
(A,B) => value A MaxMove:
(A,B,C,D) => value B-C
(A,B) => value A-B
Stategies
Sente Strategy A – B > MaxV => Sente C – D > MaxV => Reverse Sente Sente or Reverse Sente => MaxV *= 2 both => MaxV *= 4 SenteQ Strategy Always choose sente or reverse sente moves
first. Use MaxV to break ties.
MaxThreat stategy
Stategies
HotStrat: compare temperature ThermoStrat: adding all the thermographs of all
the subgame to choose the best subgame to play in.
Experimental results
Randomly choose 5 subgames (A>=B>=C>=D) 8 Strategies playing against each other (56
games one round) 100 rounds
Conclusions
Simple strategy is good enough! Hotstrat strategy is easy to implement and can
get 12% improvement.
Problems (my thoughts) Impact of imprecise evaluation? How to generalize to more than 2 plies?